The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
A communications arrangement is any network, system, or mechanism that provides for the exchange of information or data between participants. As used herein, the terms communications network, communications system, and communications mechanism are used as examples of communications arrangements. As used herein, the term “participant” refers to any device or mechanism that exchanges data with other devices or mechanisms over a communications medium.
In some communications arrangements, one of the participants is designated as a “master participant.” As used herein, the terms “master participant” and “master” are synonymous. The master participant performs one or more functions that are assigned to only the master participant and not to other participants. For example, a master participant may initiate and manage communications with other participants. As another example, the master participant may select a particular frequency-hopping scheme to be used in the communications network.
In communications arrangements with a master participant, the other participants are conventionally referred to as “slave participants.” As used herein, the terms “slave participant” and “slave” are synonymous. Communications arrangements that use a master participant conventionally use only a single master participant, with any number of slave participants. In some communications arrangements, master participants are elected from available slave participants according to a selection or voting algorithm. In other communications arrangements, master participants are the participants that initiate connections with other participants.
A frequency hopping (FH) protocol is an example of a multiple communications channel approach for wireless communications in a communications network that uses a frequency hopping signal transmission technique in which information or data is transmitted over a set of frequencies in a communications frequency band. A frequency hopping communications system is a system that uses an FH protocol. The order in which the communications network hops among the set of frequencies is known as the hopping sequence. In contrast to FH systems, a non-frequency hopping (NFH) system is simply a communications system whose carrier does not hop over a set of frequencies. A typical NFH system may occupy a portion of the communications frequency band corresponding to several frequencies used by an FH system.
With some communications system approaches, such as the FH approach, the frequency band is broken up into separate frequencies, often referred to as “communications channels.” As used herein, the terms “communication channel” and “channel” are synonymous. For example, an FH system transmits data on one channel, hops to another channel in the hopping sequence to transmit more data, and continues by transmitting data on subsequent channels in the hopping sequence. The switching of frequencies may occur many times each second.
An example of a frequency hopping protocol is the Institute of Electrical and Electronics Engineers (IEEE) 802.15.1 Wireless Personal Area Network Standard, which is based on the Bluetooth™ wireless personal area network (WPAN) technology from the Bluetooth Special Interest Group (SIG). The BLUETOOTH trademarks are owned by Bluetooth SIG, Inc., U.S.A. The Bluetooth protocol uses 79 individual randomly chosen frequency channels numbered from 0 to 78 and changes the frequencies 1600 times per second. Examples of NFH systems include the IEEE 802.11b Wireless Local Area Network (WLAN) in non-frequency hopping mode, which is the mode that typically is used, and the IEEE 802.15.3 next-generation WPAN, both of which operate in the 2.4 GHz Industrial, Scientific, Medical (ISM) band, which is an unlicensed portion of the radio spectrum that may be used in most countries by anyone without a license.
Typically, the master of an FH communications system transmits at even-numbered timeslots on the hopping sequence and the slaves listen at those regular intervals. The master will address one slave (or all slaves in a “broadcast” mode), and the addressed slave responds back to the master at the next odd-numbered timeslot. A preamble, which is known to all the participants of the FH network, is used to identify the network and for the slaves to synchronize with the master. For example, in Bluetooth and IEEE 802.15.1, the known preamble is called the “channel access code.”
A common problem for communications systems is poor transmission quality of communications channels, also referred to as poor channel performance, which results in data transmission errors. For example, poor channel performance may increase the bit error rate (BER), which results in the loss of packets, leading to reduced transmission quality and reduced throughput (e.g., the amount of information successfully transmitted and received). As used herein, a “data packet” is a block of data used for transmissions in a packet-switched system, and the terms “data packet” and “packet” are synonymous.
A common source of poor channel performance is interference from other communications systems or other interference sources. Interference has a dynamic nature due to the use of different devices at different times and locations, and as a result, eventually all channels of a communication system that uses multiple channels may experience some degree of interference at some time. Interference is largely dependent on the type of device and the device's operating characteristics. For example, cordless phones and wireless LAN's occupy different channels. Moreover WLAN may occupy one of three different subsets of channels depending on quality of service requirements. Interference may change depending on the several factors including, but not limited to, the following: the type of device, such as cordless phone or WLAN; the operation mode of the device, which determines the particular channels that are occupied; when the communications systems use the band; and the relative locations of the participants of each system to participants of other systems. Because the participants may be mobile, interference may vary depending on the movements of the participants of one system relative to the locations of participants of other systems. In addition, interference may arise from other sources resulting in a degradation of performance.
One strategy for managing poor channel performance is to increase the power used in the transmissions such that interference has less of an impact because the system is transmitting at the increased power. However, in mobile applications, this increased power approach drains batteries used by the participants, reduces the standby time of the participants, and increases recharge times. Thus, the required power increase may be impractical due to such adverse impacts. While the size of the batteries can be increased, minimizing battery size and the cost of the batteries is of concern for most mobile and wireless devices. Also, the increased power approach only benefits the system using the increased power and results in a larger interference impact on other systems. Moreover, if the other devices employ power control, the increased power approach would lead all the devices eventually to transmit using the maximum transmit power.
Other strategies for managing poor channel performance include retransmitting data that had errors and incorporating a form of redundancy into the transmission (e.g., by including multiple copies of some or all of the data) so that the participant receiving the data can identify and correct transmission errors. However, such approaches require additional resources to both identify the errors and then to correct the errors, such as by using additional transmissions or by using redundant data transmission approaches that decrease the amount of information that can be transmitted, which reduces the throughput of the communications system.
Another strategy for addressing the issues of interference, power consumption, and decreased system throughput is to employ a power control approach that changes the power on which transmissions are made (e.g., the “transmit power”) based on system performance. For example, when performance is poor, the transmit power may be increased to achieve improved performance. Similarly, when performance is good, the transmit power may be decreased to conserve power while maintaining performance at acceptable levels.
One power control strategy adjusts the transmit power for the communications arrangement based on the performance of the communications channels used by the communications system. The change in the communication system's transmit power may be determined by a number of approaches. For example, one approach is to ensure adequate performance on all communications channels using the performance of the worst communications channel to set the transmit power (e.g., a so-called “lowest common denominator” approach). However, the increased transmit power for the communications arrangement is not needed for channels that do not require the extra power for suitable performance, resulting in increased power consumption.
Another approach for determining the transmit power of a communications system is to select the transmit power for the communications arrangement so that at least a specified number of channels have acceptable performance. This can minimize power consumption on communications channels that do not need an increase in transmit power for adequate performance. However, other communications channels will generally have unacceptable performance, thereby reducing the throughput of the communications system because such communications channels often fail to provide for successful communications. Furthermore, due to the dynamic nature of interference on multiple communication channel systems, it may be difficult to ensure that a suitable number of communications channels have acceptable performance while trying to minimize power consumption.
Another power control approach uses received signal strength indicator (RSSI) to measure performance. For example, the RSSI of a communication is measured and compared to a specified RSSI value. If the measured RSSI is greater than the specified RSSI value, the transmit power is reduced to conserve power. Conversely, if the measured RSSI is less than the specified RSSI value, the transmit power is increased to provide adequate performance, albeit at the expense of increased power consumption.
However, a difficulty with the RSSI approach is that while the RSSI may be high due to a strong signal of interest, the RSSI also may be high due to a strong interference signal, such as another device located close by the participant receiving the communication. Therefore, in circumstances with high RSSI from a strong interference source, the transmit power may be reduced to conserve battery resources, resulting in decreased performance because of the bigger impact of the interference source on the subsequent reduced power communications.
Based on the need for wireless communications and the limitations in the conventional approaches, an approach for managing power for communications channels that does not suffer from the limitations of the prior approaches is highly desirable.